Traditional high-dose external beam radiation treatment and prolonged low-dose radiation treatment (brachytherapy) are well-established therapies for the treatment of cancer, a malignant form of cellular proliferation. Brachytherapy is a form of radiation treatment in which a radiation source is placed into or adjacent to a malignant tumor. There are two general categories of brachytherapy: high dose rate (HDR) and low dose rate (LDR). HDR brachytherapy typically involves the placement of a high-activity radiation source adjacent to or into the malignant tumor for a limited period of time. LDR brachytherapy involves the placement of a low-activity radiation source adjacent to or into the malignant tumor for an indefinite period of time.
The implantable low activity radiation sources are typically quite expensive. In particular, the source may only be effective for radiotherapy during a relatively brief period of time during which the radioactivity is provided at a useful therapeutic level. Depending on the radioisotope used, the decay time may be as short as hours, days or weeks.
Brachytherapy devices for treatment of localized lesions such as tumors of the prostate, breast, brain, eye, liver, spleen, or the like, commonly employ radioactive “sealed source” seeds. The term “sealed source,” as used herein, means that radioisotopes incorporated into a device are integral with the device and are not released from the host material of the device in the environment of usage. A typical sealed source seed includes a radiation source encapsulated within a substantially impermeable, biocompatible capsule made of, for example, titanium that is designed to prevent leakage or release of the radioisotope. The seeds are typically about 0.50 to 0.85 mm in diameter and about 4 to 10 mm long. These seeds are implanted individually at a treatment site within and/or around a lesion, typically with a medium-bore 18-gauge delivery needle.
The radiation sources used in LDR brachytherapy are radioactive isotopes. Common isotopes used are 103Pd (Palladium), 125I (Iodine), 198Au (Gold), and 192Ir (Iridium). The isotopes used in LDR brachytherapy are chosen for their low energy and short half-life. Low energy provides for limited penetration of the radiation so that the radiation effect is limited to the tumor without affecting adjacent normal tissue. A short half-life is desirable so that the radiation dose can be delivered in a reasonably brief period of time.
For 103Pd and 125I, the zone of therapeutic effect is limited to about a 1-cm diameter sphere around the seed. Typically, a three-dimensional array of seeds is used to treat a tumor. In LDR brachytherapy of prostate cancer, over 100 seeds are typically used. Because solid tumors, such as those found in prostate cancer, are viewed to be diffused, the entire organ is targeted.
Conventionally, a medical operator places multiple seeds into a three-dimensional array with a needle using a two-dimensional grid pattern, and longitudinal spacing. A needle guide called a template typically defines the two-dimensional grid. The template includes a matrix of holes, which guide the longitudinal advancement of the needles to insure their proper two-dimensional positioning in the tumor. Subsequent to establishing the two-dimensional array of needles in the tumor, the medical operator deposits the seeds along the longitudinal axis of each needle. Biocompatible spacers typically space the seeds along the longitudinal axis of the needle. The medical operator alternately inserts spacers and seeds into the needle prior to placing the needle into the tumor. To maintain the position of the line of seeds and spacers as the needle is withdrawn, the medical operator typically employs a mandrel. This leaves a line of seeds in their proper longitudinal position. The medical operator then repeats this process at the other two-dimensional grid coordinates forming the desired three-dimensional array of seeds.
LDR brachytherapy is an effective modality for treating localized malignancies, however, it is not always successful in eradicating the malignancy. Disadvantages of the use of such seeds as radiotherapy devices typically include their nature as discrete sources of radiation, and the corresponding discrete nature of the dosages that they provide. To provide an effective radiation dose over an elongated or wide target area, the seeds should be uniformly and relatively closely spaced. The need to ensure accurate and precise placement of numerous individual radiation sources undesirably prolongs the exposure of the medical operator and the surgical team to radiation. Moreover, the use of discrete seeds requires an elaborate grid matrix for their proper placement. This requirement is labor-intensive and costly. In addition, the discrete nature of the seeds renders them more susceptible to migration from their intended locations, thereby potentially subjecting portions of the lesion, the treatment site, and surrounding healthy tissue to over- or under-dosage, reducing the effectiveness and reliability of the therapy.
In an attempt to accomplish a more even distribution of radioactive seeds in a longitudinal direction, the so-called “rapid strand” approach provides a bioabsorbable strand or suture onto which several radioactive seeds have been pre-assembled in a uniform spacing approximately 10 mm apart. Unfortunately, although spacing the seeds along the strand can generally provide a somewhat more uniform longitudinal radiation dosage to the patient, the strand itself may not be sufficiently rigid to allow for it to be properly and reliably installed at the treatment site without becoming jammed in the delivery needles. In addition, because the seeds are the source of the radiation, as mentioned above, the radiation dose provided thereby has the limitations associated with the discrete nature of the seeds.
Further, medical operators typically use 18-gauge bevel-tip needles to place brachytherapy seeds. Due to the bevel tip and flexibility of the hypodermic tubing of the 18-gauge needle, such needles tend to splay making it necessary for the medical operator to make multiple sticks to place the needle in the desired location.